1. Field
The present invention relates to projection-type image display apparatuses projecting enlarged images shown on display devices onto screens, and in particular, relates to projection-type image display apparatuses including structures for cooling the display devices, light-source lamps, or the like.
2. Description of the Related Art
Projection-type image display apparatuses enlarge images shown on display devices such as small cathode-ray tubes (CRTs) or light valves (small display devices capable of storing and removing the images in real time) through projection lenses and project the images onto screens.
Among such display devices, liquid-crystal devices as well as the small CRTs are in widespread use. The projection-type image display apparatuses including the liquid-crystal devices serving as the display devices are often referred to as liquid-crystal projectors.
The display devices can be grouped under a reflective type and a transmissive type. In the projection-type image display apparatuses including the reflective display devices, light beams from light sources are incident on the front surfaces of the display devices, and are reflected from the display devices. The projection-type image display apparatuses enlarge the reflected light beams through optical systems such as lenses, and project the light beams onto screens.
On the contrary, in the projection-type image display apparatuses including the transmissive display devices, light beams from light sources are incident on the rear surfaces of the display devices, and are transmitted through the display devices. The projection-type image display apparatuses enlarge the transmitted light beams through optical systems such as lenses, and project the light beams onto screens.
Both the reflective and transmissive types of liquid-crystal display devices have been already put into practice.
Additionally, display devices referred to as digital micromirror devices (DMD) have also been developed, and are employed in the projection-type image display apparatuses. The DMDs include minute mirrors on the front surfaces of the display devices, and the number of mirrors is the same as that of the pixels. The light beams entering the front surfaces of the DMDs are modulated and reflected by electronically and mechanically changing the angles of the individual mirrors. That is to say, the DMDs are of a reflective type.
The projection-type image display apparatuses that apply light beams from the light sources to the front surfaces of the DMDs and that project the modulated light beams reflected from the surfaces of the DMDs onto screens through the optical systems such as the lenses are often referred to as digital light processing (DLP™) projectors. The DLP is a trademark of Texas Instruments Incorporated in the United States of America.
The recent development in high-brightness technology in addition to high-resolution technology of the projection-type image display apparatuses including the liquid-crystal devices or the DMDs has been remarkable. Up to now, in order to use the projection-type image display apparatuses, the brightness in rooms needed to be reduced by, for example, closing curtains. However, due to the high-brightness technology, the projection-type image display apparatuses are available under ordinary indoor brightness substantially without trouble.
The high-brightness technology is achieved by a technology of a reduction in loss of light transmission systems and by an increase in the amount of emission of the light sources themselves.
Due to the increase in the amount of emission of the light sources, the amount of heat generated in the interiors of the projection-type image display apparatuses is increased. Meanwhile, components in the projection-type image display apparatuses must be highly densified due to user demands for compact profiles.
Therefore, the development in technology for efficiently cooling the increasing heat even with the highly densified layout of the components has become essential.
U.S. Pat. Nos. 6,644,817, 6,402,324, and 6,350,033 disclose technologies for cooling projection-type image display apparatuses including transmissive liquid-crystal devices serving as display devices.
The projection-type image display apparatus disclosed in U.S. Pat. Nos. 6,644,817 or 6,402,324 includes two intake fans for drawing outside air disposed at the front left and the front right of the casing of the apparatus, and two exhaust fans for discharging the air disposed at the rear. The apparatus further includes three air intakes, two of which are formed in front of the intake fans and the rest is formed in the bottom center.
The fans and the air intakes form first and second flow channels in which air flows from the front to the rear along the left and right side surfaces of the casing of the projection-type image display apparatus, and also form a third flow channel in which air flows from the bottom center to the rear.
Moreover, in the projection-type image display apparatus, two separate power-supply units are disposed at the left and the right of the casing. These two power-supply units are cooled by the first and second flow channels.
A light-source unit generating the most heat is disposed in the rear of the casing adjacent to the exhaust fans, and cooled by the third flow channel in addition to the first and second flow channels.
Furthermore, a structure for cooling three transmissive liquid-crystal devices corresponding to red, green, and blue (RGB) colors included in the projection-type image display apparatus is disclosed in U.S. Pat. No. 6,350,033. The transmissive liquid-crystal devices generate heat since part of the optical energy of the transmitted light beams is converted into the thermal energy as a transmission loss. Accordingly, an additional intake fan for cooling the transmissive liquid-crystal devices forcedly circulates the air inside a sealed space accommodating the transmissive liquid-crystal devices so as to cool the air.
U.S. Pat. No. 6,682,197 discloses a technology for cooling a projection-type image display apparatus including reflective liquid-crystal devices.
According to an embodiment of the projection-type image display apparatus disclosed in U.S. Pat. No. 6,682,197, the projection-type image display apparatus includes one large exhaust fan and two relatively small intake fans. Furthermore, three separate reflective liquid-crystal devices are disposed at three remote positions.
One of the intake fans is disposed adjacent to one of the three reflective liquid-crystal devices so as to cool this reflective liquid-crystal device substantially exclusively.
The other intake fan and the large exhaust fan cool the other two reflective liquid-crystal devices and a light-source unit generating the most heat.
The light-source unit includes a light-emitting element and a substantially paraboloidal metallic reflector covering the light-emitting element. The cooling air cools the reflector and the light-emitting element whose heat is transferred to the reflector by flowing along the rear surface of the metallic reflector.
The two reflective liquid-crystal devices and the reflector of the light-source unit are not arranged in a line, but a duct structure is formed by appropriately disposing casing members and guiding plates for the cooling air. Thus, the two reflective liquid-crystal devices and the light-source unit are cooled by the intake fan and the exhaust fan disposed at the inlet and the outlet of the duct structure.
Since light-source units generate the most heat in projection-type image display apparatuses, extra high cooling capacity for the units is required for high-brightness projection-type image display apparatuses.
Also, display devices such as DMDs and liquid-crystal devices generate heat when semiconductor elements drive pixels. In addition to the self-heating, reflective display devices generate heat due to a reflection loss, and transmissive display devices generate heat due to a transmission loss.
The heat due to the reflection loss or the transmission loss is increased relative to the amount of emission of the light sources. Accordingly, the cooling of the display devices as well as the cooling of the light-source units is essential as the brightness of the projection-type image display apparatuses is increased.
On the other hand, as the resolution of the recent projection-type image display apparatuses has been improved, there has been an increasing need for viewing not only slides and still images as in conventional art but also movies and music videos. Thus, a technology for reducing noise generated by, for example, fans is also required in addition to the cooling technology.
According to the cooling technologies disclosed in U.S. Pat. Nos. 6,644,817, 6,402,324, and 6,350,033, not only optical components such as the light-source units and the transmissive display devices but also the power-supply units and control circuit boards are arranged suitable for cooling. However, the arrangements are not applicable to projection-type image display apparatuses having different circuit configurations or modes.
Furthermore, since four or five intake and exhaust fans are required for cooling, improvements in terms of the noise must be introduced.
According to the cooling technology disclosed in U.S. Pat. No. 6,682,197, the duct structure is formed of the casing members and the guiding plates for the wind direction. The light-source unit and the reflective liquid-crystal devices disposed inside are efficiently cooled by the cooling air passing through the duct structure.
However, since the projection-type image display apparatus disclosed in U.S. Pat. No. 6,682,197 includes the intake fan and the exhaust fan at the front left and the front right thereof, the duct structure connecting the intake fan and the exhaust fan is not linear, and includes a plurality of bending portions and wind-direction guides at certain positions thereof.
As a result, it is estimated that the pressure loss of this duct structure will be high compared with that of a linear duct structure. Therefore, if the heat generated by the light-source unit and the display devices is increased due to the high brightness, there is a possibility of insufficient cooling capacity caused by insufficient air volume unless the number of the fans or the power of the fans is increased. In addition, noise is increased with the number of the fans or the power of the fans.